Method for accessing stations onto a common transfer medium and network station for carrying out said method

ABSTRACT

The invention relates to a method for accessing stations (WT, AP, APTi) onto a common transfer medium, wherein said stations (WT, AP, APTi) share the common transfer medium with other stations. In order to apportion the available transfer capacity as efficiently as possible, said stations inform each other of their capacity needs by sending messages when necessary. The sent messages can contain information on priority and capacity requirement. Stations which receive the sent capacity requests release unrequired transfer capacity or transfer capacity which is not urgently required, so that said capacity can by used by a station in need. The corresponding information can also be transferred by other stations, e.g. by several hops.

[0001] Method for the accessing by stations of a common transmissionmedium and a network station for performing said method

[0002] The invention relates to a method with the features recited inthe preamble of Claim 1 whereby stations may access a commontransmission medium, and to a network station for performing saidmethod.

[0003] In communication systems such as GSM (Global System for MobileCommunication), UMTS (Universal Mobile Telecommunication System), andHiperLAN (LAN: Local Area Network), mobile stations communicate withnetwork-side stations over radio interfaces. The radio interfaces canhere be employed by a plurality of mobile stations in parallel orconcurrently. The accessing by stations of a common transmission mediumof this type is facilitated by multiple access (MA) systems, whereby adistinction is made as to whether the medium is divided among thestations on a Time Division Multiple Access (TDMA) basis, a FrequencyDivision Multiple Access (FDMA) basis, a Code Division Multiple Access(CDMA) basis or a Space Division Multiple Access (SDMA) basis. Themedium is frequently subdivided into frequency channels and/or timeslots, such as in the case of GSM, TETRA (Trans-European Trunked Radio),and DECT (Digital European Cordless Telecommunications). Measurementsare employed in the case of systems coordinated on a decentralized basisto determine whether a channel can be used. In keeping with the radiopropagation it is possible to re-use a channel, for instance at anappropriate spatial distance.

[0004] Future radio systems should be able to support a large number ofdifferent services simultaneously. The services differ in having, forexample, different transmission requirements in terms of delay or errorrate, for instance, and arrival processes. The aim of the carrier is tomaintain the quality-of-service agreed during connection setup and touse the available spectrum as efficiently as possible.

[0005] An occurrence in communication systems coordinated on adecentralized basis whose channel assignment is based on radio channelmeasurements is for a station to require transmission capacity for aconnection but for this transmission capacity to be unavailable, theneighboring stations having occupied this capacity or the relevantchannel. As a consequence, either the connect request has to be rejectedor the agreed quality-of-service of existing connections cannot bemaintained. In communication systems with link adaptation, such asEDGE/EGPRS (Enhanced Data Rates for GSM Evolution/Enhanced GeneralPacket Radio Service), the occupation of a channel by a neighboringstation may necessitate a change of modulation/coding, thereby reducingthe available data rate and consequently negatively affecting existingconnections.

[0006] A particular occurrence when connections with differentquality-of-service requirements are operated simultaneously is for dataservices with low-level requirements, such as file transfers (FTP/FileTransfer Protocol downloading), to require and occupy more transmissioncapacity during connection setup than is necessary to maintain thequality-of-service required by the user if this is available at thattime, for example if a file transfer is being performed. The relevantcapacity will then cease to be available at the neighboring stations andconnect requests will have to be rejected.

[0007] There is therefore the problem of distributing the existingtransmission capacity among radio cells organized on a decentralizedbasis as efficiently as possible, whereby, on the one hand, the capacitymust be utilized as fully as possible even if this results in exceedingthe required quality-of-service, and, on the other hand, anynon-essential capacity can, if necessary, be made available to otherradio cells.

[0008] This problem arises in systems in which services with differentquality-of-service requirements share the common radio medium and inwhich use is made of measuring, dynamic channel assignment organized ona decentralized basis. The specific type of channel, such as time slotand/or frequency channel, is basically not of crucial significance here.There are currently various systems of this type:

[0009] In the IEEE 802.11 standard there is a mode controlled on acentralized and a decentralized basis. In the case of decentralizedcontrol (Distributed Coordination Function (DCF)), all stations are peerentities and service prioritizing is not supported. In the case ofcentralized control (Point Coordination Function (PCF)), accessing bythe individual stations in a radio cell is controlled by a centralstation serving as the access point (AP), with several access pointsbeing connected via a distributed system (DS). The problem describedwill not be resolved if the access points are unable to communicate witheach other, for example if the central controller (PCF) is used by astation without access to a distribution system (DS) in order to supporta specific quality-of-service in an ad hoc mode. With decentralizedaccess, the transmission of a single packet could be controlled by meansof a priority specified according to, among other things, therequirements of the quality-of-service. However, this is currently notsupported by the standard.

[0010] In the HIPERLAN/2 system for data networks currently beingstandardized, a base station (Access Point (AP)) manages the access tothe common medium by the cordless stations (Wireless Terminal, WT)registered with it. Several base stations can be coordinated by ahigher-order instance (Access Point Controller (APC)). The standard onlyallows for central administration of the transmission capacity withinthe area of an access point. If an access point does not have aconnection to the fixed network, the access point is referred to as acentral controller (CC).

[0011] The object of the invention is to distribute the existingtransmission capacity as efficiently as possible with a method for theaccessing by stations of a common transmission medium by means of amultiple access system, or to propose a station for performing saidmethod.

[0012] This object is achieved by means of a method with the features ofClaim 1 whereby stations access a common transmission medium, and bymeans of a station with the features of Claim 11 for performing saidmethod.

[0013] Advantageous embodiments are the subject of dependent claims.

[0014] Stations sharing a common transmission medium with other stationsadvantageously inform these, when required, about their capacityrequirements by sending messages over the radio interface or over, inH2GF for example, defined interfaces between the network-side stationsor access points. The messages that are sent can contain informationabout the priority and the capacity needs. Stations receiving the sentcapacity requests release any transmission capacity that is not needed,or not urgently needed, so that this can be used by the needy station.The relevant information can also be forwarded via other stations overseveral “hops”, for instance.

[0015] A method that is also particularly advantageous is one wherebythe information is exchanged by means of an easily detectable signal, inparticular an energy pulse. The easily detectable signal can topractical effect be evaluated by other systems, in particular with adifferent coding system, different code, different modulation system,different bandwidth and/or different frequency band. It is also possiblehere to use discriminating variables with the aid of which stations ofdifferent carriers are distinguished.

[0016] Exemplary embodiments are explained in greater detail below withreference to the drawing.

[0017]FIG. 1 is a schematic representation of an arrangement of radiocells in which stations share a common transmission medium according toa first exemplary embodiment,

[0018]FIG. 2 is a schematic representation of an arrangement accordingto a second exemplary embodiment, and

[0019]FIG. 3 is a schematic diagram for clarifying an exemplary flow.

[0020] As can be seen in FIG. 1, an exemplary radio communication systemconsists of one or, as shown here, several radio cells Z advantageouslypartially overlapping. Within these radio cells Z, on the network-sidethere is in each case a base station or access point AP coordinating theradio traffic within the relevant radio cell Z. The radio interfacebetween said network-side stations AP, APT, and stationary or mobilestations or, as the case may be, wirelessly linked terminals WT of auser is set up via transmit and receive equipment. This transmit andreceive equipment is a constituent part of the base stations or accesspoints AP or is linked to these. It can in particular also be aconstituent part of access point terminals APTi, APTj, APTk with (i, j,k=1, 2, 3 . . . ), several of which can be located in a cell Z or groupof cells Z as substations of the access points AP.

[0021] In the exemplary embodiments a central network-side station, suchas the access station AP, coordinates transmission in its vicinity or inits area of influence by assigning transmission capacity for example tothe stationary or mobile stations or, as the case may be, terminals WTserved by it. If the central network-side station AP requires moretransmission capacity than it momentarily occupies and no free channelsare available, it will inform the network-side stations APi, APj, APk(i, j, k=1, 2, 3, . . . ) in its vicinity about the shortage oftransmission capacity by sending a relevant message over the radiointerface.

[0022] This message can be transmitted in such a way as to be easilydetectable, for example in the form of a synchronizing sequence, and/orallow conclusions to be drawn concerning the priority of therequirements and the required transmission capacity. Simple messagesthus require no decoding but only have to be detected.

[0023] The message can also contain additional parameters, in that caserequiring decoding at the receiving station.

[0024] Other network-side stations Api, Apj, APk, in particular centralstations, which receive this message will release any non-urgentlyrequired transmission capacity, which is to say in particular channels,used for services with low-level requirements, for example for what arecalled “best effort” services, or will, where applicable, switch toanother channel so that this is available to the needy station AP.

[0025] To increase the range of the message, according to a particularlypreferred embodiment this can also be forwarded from other stations,such as from radio-controlled network-side or mobile terminals WTsserved by the central station AP.

[0026] In the first exemplary embodiment, as can be seen from Table 1 inFIG. 1, in the currently standardized radio access system HIPERLAN/2(H/2) the radio resources are assigned to the network-side base stationsor access points AP in the form of frequency channels 1-6. An accesspoint AP consists here of one or more transmit units APT (Access PointTransceiver) and a controller APC (Access Point Controller). Theassignment can analogously also be made to cells Z or access pointterminals APT. The channel assignment can be coordinated centrallywithin the area of a network-side controller APC. Communication forcoordinating the frequency assignment is currently not provided betweendifferent APCs.

[0027] Each transmit unit or, as the case may be, each access point APTemploys dynamic frequency selection (DFS) to occupy a frequency channelhaving maximum reutilization spacing in order to achieve low-levelinterference power.

[0028] Capacity meeting present requirements is assigned to usersdynamically by allocating time slots within the media access control(MAC) frame. So that the necessary quality-of-service can also bemaintained in unfavorable transmission conditions, use is made of, forexample, adaptive modulation/coding, known in its own right as, forexample, ‘link adaptation’. This means that higher-level coding and/orlower-value modulation is used if channel characteristics are relativelypoor, although the available data rate will be reduced as a result. Toincrease the available data rate, the interference of the radio channelhas to be reduced.

[0029] If the affected access point AP is unable to switch to anotherfrequency channel, a message will be transmitted to the cells with thesame used channel or, as the case may be, co-channel cells, with themessage indicating the shortage of capacity. For the access points APreceiving this message there are various possibilities for supportingthe affected access point AP.

[0030] Switching to another frequency channel is a first possibility. Asthe interference is reduced, the affected access point AP can usehigher-value modulation.

[0031] It is also possible to reduce transmissions to what is necessaryin order to comply with the service agreements, for example theso-called Quality-of-Service (QoS). Where applicable, it is alsopossible to switch to a lower-rate physical operating mode (PHY mode),thereby reducing the transmit power. The data rate can also be increasedwhen use is made of suitable algorithms for link adaptation.

[0032] According to another embodiment, neighboring base stations can beinduced to release occupied channels in the case of systems whichgenerate channels through a combination of frequency division and timedivision multiple access (FDMA/TDMA) and in which channel capacity isassigned by occupying/releasing individual channels.

[0033] A first embodiment is shown in FIG. 1, the flow being apparentfrom FIG. 3. After a connect request from the user, the user's stationWT requests a channel for additional transmission capacity from theaccess point terminal APT3 with which it is communicating. However,there is no channel here, for instance, that can be freely occupiedbecause all channels have been assigned to specific base stations or, asthe case may be, access points or cells, as can also be seen from Table1 in FIG. 1.

[0034] It is determined on the network side whether there is sufficienttransmission capacity to assign a suitable channel to the requestingstation WT. This not being the case here, the access point terminal APT3sends a capacity request (Capacity request(prio)) to the neighboringaccess point terminals APTi, APTj, APTk (i=1, 2, 4, 5). The capacityrequest (Capacity request(prio)) advantageously also contains prioritydetails, ‘prio’, enabling the receiving access point terminal APTi,APTj, APTk to determine the urgency or the quality-of-service of therequest.

[0035] It is then determined in the receiving access point terminalsAPTi, APTj, APTk whether these are able to release suitable transmissioncapacity. If they can, for example in the case of access point terminalAPT2, this will be done, channel 3, for example, being released here asshown in Table 2 in FIG. 1.

[0036] The access point terminal APT3 requesting transmission capacityor, as the case may be, access point AP continuously monitors thecapacity status on the radio interface. As soon as it finds a freechannel, or one that has become free, in this case channel 3, whichmeets the required conditions, it sends a connect confirm signal to therequesting station WT. This confirms the connection capability, in turn,of the requesting function or equipment. The channel 3 that has becomefree is thus occupied by the access point terminal APT3, as shown inTable 3 in FIG. 1.

[0037] A corresponding notification about release and/or non-release canalso optionally be sent by the access point terminals APTi, APTj, APTkto the inquiring access point terminal APT. This will then not have tocontinuously monitor the radio interface.

[0038]FIG. 2 shows an embodiment in which forwarding takes place.However, none of the other access point terminals APTi respond to therequest for transmission capacity from the access point terminalAPT3—step 1 a—because the cells Z do not overlap to a sufficient extent.

[0039] In another step 1 b, the information is consequently forwardedfrom the stationary and mobile stations or, as the case may be,terminals WT, which are located in the corresponding area and which areoutlined in the lower picture in FIG. 2 as circles in the edge region ofthe cell. In the present example in Table 2 in FIG. 2, the access pointterminal APT2 can release transmission capacity in response to therequest: channel 3, for instance. The base station or, as the case maybe, the access point terminal APT3 originally requesting capacityrecognizes this and re-occupies, according to Table 3 in FIG. 2, channel3 as in the preceding exemplary embodiment.

[0040] Both embodiments thus permit variable channel assignment wherebyuse of the same channel by two neighboring cells or base stations isavoided and optimized utilization of the available channels nonethelessfacilitated.

1. Method for the accessing by stations (WT, AP, APTi) of a commontransmission medium in a radio communication system, whereby thestations (WT, AP, APTi) share the common transmission medium with otherstations, wherein one of the stations (WT, AP, APTi), when required,informs at least one neighboring station outside its own cell (Z) aboutits capacity requirements by sending at least one item of information.2. Method according to claim 1, wherein the information is receivedand/or forwarded by stations (WT, AP, APTi) embodied as user-sidestations (WT) or network-side stations (AP, APT).
 3. Method according toclaim 1 or 2, wherein a station (APT2) with releasable capacity releasesa transmission channel.
 4. Method according to a preceding claim,wherein a capacity-requesting station (APT3) continuously monitors thecapacity status on the transmission medium and/or receives notificationof capacity release from the releasing station (APT2).
 5. Methodaccording to one of the preceding claims, wherein the informationcontains a capacity request.
 6. Method according to claim 5, whereinpriority information is transmitted along with the capacity request. 7.Method according to claim 5 or 6, wherein the capacity request isforwarded via other stations (WT).
 8. Method according to one of thepreceding claims 5 to 7, wherein the capacity request depends on thechoice of different services with different quality-of-servicerequirements shared by the common transmission medium.
 9. Methodaccording to one of the preceding claims 5 to 8, wherein the capacityrequest depends on the choice of different services with differentquality-of-service requirements for which use is made of measuring,dynamic channel assignment organized on a decentralized basis. 10.Station for performing a method according to a preceding claim.